MOLECULAR-STRUCTURE AND INTERNAL MOTION IN THE (CO2)(3)CENTER-DOT-CENTER-DOT-CENTER-DOT-HCN TETRAMER

The molecular structure and energetics of the (CO2)(3)...HCN tetramer are determined at the ab initio Hartree-Fock (HF) level of theory empl oying the split-valence 4-31G and double zeta plus polarization functi on (DZP) basis sets. Electron correlation effects are accounted for by second-order Moller-Plesset perturbation theory (MP2) in single point calculation at the optimized HF/DZP geometry. The HCN molecule is pre dicted to interact with a non-planar (CO2)(3) trimer via the nitrogen end, in agreement with a recent Fourier transform microwave study. The internal motion in the (CO2)(3) non-planar subunit has also been exam ined. The energy barrier for rotation of the CO2 monomers around one o f their symmetry axes is found to be 844 cm(-1) (HF/4-31G value), whic h may inhibit tunneling motion through a planar (CO2)(3) arrangement.